Dark Spots (Possibly Rust) On Pebble Tec/ Diamond Bright

[johnboy85]

Hey guys I have had an issue with these dark spots in the pool since I've bought this house and they seem to be multiplying. I have tried vitamin C tablets on them and it has had no effect. I purchased the following device to use with muriatic acid but that also has had no effect.
https://www.amazon.com/Purity-Pool-...925&sr=8-1-fkmr0&keywords=pool+rust+spot+acid

I used a stainless steel brush and brushed like crazy, it did not do a thing on them. My pool was built in 92' I notice when I use the larger 18" stainless steel brush I find sand/ pebbles in the robotic cleaner. Does anyone else have this problem with pebble tec/ diamond bright?

I tried a thick sharp edge paint scraper on one of the spots and it lighted up drastically by just scraping at the top layer. Should I try a concrete file and see if I can file the spots out? Is this advisable?

Below are pictures of the spots and the tool I am thinking about using.


Also below are my pool levels (I just got done slamming)
FC 10
CC 0
CH 250
TA 140
CYA 35
PH 7.8

I plan on lower TA once FC is lower.

 

[BoDarville]

Let's make sure it is not black algae. To test, gently scrape a sample of the suspected black algae (preferably with your fingernail - but however you can get a sample) and then smudge it on plain white paper. If the smudge scrapes off and is a greenish color, then it’s black algae.

 

[kimkats]

That ^^^^^^^^^^^^^ It will not be easy but well worth your effort. We can fix it if it is black algae!

Kim:cat:

 

[zea3]

You can try scrubbing them with a trichlor puck and see if that lightens the stain.

 

[duraleigh]

Those spots are puzzling. I agree with BoDarville that black algae is a possibility.

If you eliminate that, then you may have to scrape them but make that a last resort as you essentially scrape off the surface of your pool.

 

[pooldv]

If it isn't black algae try some wet/dry sandpaper.

 

[johnboy85]

Thanks Guys, I have had black algae and was able to scrap off those black spots with ease with a stainless steel brush. Below is a picture of black algae I had on my steps. These other spots are something completely different.

 

[kimkats]

Well you know what to do then........start sanding with the wet/dry sandpaper.

Kim:cat:

 

[wjr75]

Has anyone shot off any fireworks over your pool lately?

 

[johnboy85]

Before I purchased the home renters were living here. A few years back during hurricane season the renters threw the patio future into the pool to avoid the furniture being blown through the sliding glass doors. The furniture must have been in the pool long enough to cause rust stains. We also had the roof replaced when we moved in and a lot of debris got into the pool. The pool screens need to be repaired and I noticed when we treated the yard with granular some of it was blown onto the pool deck. A number of things could have caused these stains, I am almost positive they are rust stains. Some of the black spots have brown in them which makes me think rust. The problem is how porous this pebble tec/diamond bright finish is which makes it difficult for vitamin c or muriatic acid to be viable option without draining the entire pool. I was under the impression this type of finish was rust resistant. The only thing that seems to work at removing the spots is to scrap at the top surface. I think I will try some wet/dry sand paper before using the aggressive file I have.